Steels resistant to stress corrosion cracking

ABSTRACT

A chromium steel having good resistance to stress corrosion cracking comprises by weight from 0.01 to 0.2 percent carbon, from 0.01 to 2.0 percent silicon, from 0.01 to 4.0 percent manganese, from 1.0 to 5.0 percent nickel, from 12.0 to 20.0 percent chromium, from 0.5 to 2.5 percent molybdenum, from 0.1 to 2.0 percent niobium, 0.01 to 0.1 percent nitrogen and iron the balance apart from normal impurities.

United States Patent Kirkby et al.

[ 5] Mar. 14, 1972 STEELS RESISTANT TO STRESS CORROSION CRACKING Inventors: Henry William Kirkby, 17 Furniss Avenue, Totley Rise, Sheffield; John Edmund Truman, 14 Park Avenue, Chapeltown, both of England Filed: Aug. 15, 1968 Appl. No.: 752,771

Foreign Application Priority Data Aug. 16, 1967 Great Britain ..37,795/67 US. Cl. ..75/l28 G, 75/128 N, 75/128 W Int. Cl ..C22c 39/20 Field olSearch ..75/128.6, 128.9, 126 C, 126.1,

References Cited UNITED STATES PATENTS l/l937 Franks ..75/128.6

FOREIGN PATENTS OR APPLICATIONS 212,628 1/1958 Australia ..75/128.6

Primary Examiner-Byland Bizot Attorney-Buell, Blenko and Ziesenheim [5 7] ABSTRACT 4 Claims, No Drawings STEELS RESISTANT TO STRESS CORROSION CRACKING The present invention is concerned with steels containing from 12 to 20 percent of chromium which are resistant to stress corrosion cracking.

Under certain conditions, 18/8 austenitic steels are very prone to stress corrosion cracking, particularly where chloride-bearing environments are encountered and where operating temperatures are in excess of the ambient temperature. Resistance of this type of austenitic steel to stress corrosion cracking can be increased by raising the nickel content but this also increases the cost considerably.

Iron containing from 17 to 20 percent of chromium displays excellent resistance to stress corrosion cracking. However such chromium irons develop a coarse-grain structure which gives rise to brittleness, if heated to above about 900 C. as occurs at a weld. Furthermore, welding reduces the resistance to corrosion and as a result further heat treatment is necessary after the welding process.

The present invention provides a steel comprising, by weight, from 0.01 to 0.2 percent carbon, from 0.01 to 2.0 percent silicon, from 0.01 to 4.0 percent manganese, from 1.0 to 5.0 percent nickel, from 12.0 to 20.0 percent chromium, from 0.5 to 2.5 percent molybdenum, from 0.1 to 2.0 percent niobium, from 0.01 to 0.1 percent nitrogen.

Preferred proportions of the nonferrous components of the alloy are, by weight, from 0.02 to 0.06 percent carbon, from 0.25 to 0.7 percent silicon, from 0.3 to 1.0 percent manganese, from 2.0 to 3.0 percent nickel, from 15.0 to 17.0 percent chromium, from 0.8 to 1.2 percent molybdenum, from 0.4 to 0.7 percent niobium and from 0.02 to 0.04 percent nitrogen.

It has been found that the steels of the present invention show improved properties compared with 18/8 austenitic steels and conventional 17-20 percent chromium iron. The steels of this invention retain the very high resistance of the 17-20 percent chromium irons to stress corrosion cracking but may also be welded with insignificant grain growth to give no necessity for a post welding heat treatment. In addition, the general corrosion resistance in chloride environments is improved until it approaches that of the 18/8 steels.

The properties of the steels of this invention are illustrated in the following Examples.

EXAMPLE 1 Mo Nh N,

Cast A 0.05 0.53 0.57 2.49 15.65 0.99 0.66 0.028

Case B 0.02 0.49 0.60 2.50 15.64 0.97 0.50 0.039 CastC 0.05 0.50 0.57 2.49 15.65 0.99 0.66 0.030

The stress corrosion cracking resistance was demonstrated by the following results of tests in the often used reagent 42% magnesium chloride solution at boiling point. Uniaxially loaded specimens were used with a stress of 20 tons/square inch.

Steel Time to Rupture Cast A 500 hours not failed Cast B 1,015 hours not failed Cast C 500 hours not failed 17% Cr 500 hours not failed En58E 2 hours-ruptured The steel 17% Cr is a 17 percent chromium iron, and the steel en58E" is an example of an 18/8 austenitic steel.

EXAMPLE 2 Steel 3% Sodium chloride 10% Sodium chloride Cast B 0.0000 gJcm. 0.0016 gJcm.

Pitted 17% Cr 0.0016 gJcm. 0.0035 gJcm.

severe pitting severe pitting En58E 0.0000 g.lcm. 0.0004 gJcm.

slight pitting EXAMPLE 3 The weldability of the steel was demonstrated by welding three-fourths inch diameters bars using nickel base alloy electrodes. Welds were also produced in 10 gauge sheet using nickel base electrodes and the electric arc process, and autogencously by the inert gas shielded, tungsten electric arc process. In both cases bend tests through over a radium of lit, where t is the thickness of the sample, were made without any cracking of parent metal, weld or heat afifected zone. Samples of Cast C, of the composition given in Example 1, were prepared with the weld bead at midparallel. Tensile tests on these samples gave the following results.

None of the welded samples showed any sign of intergranular corrosion after 3 days at boiling point in the standard sulphuric acid/copper sulphate test reagent.

The invention also provides articles whenever made from the alloys described above.

We claim:

1. An iron-chromium based alloy for use in an article involving stress corrosion and welding consisting essentially of the following elements in the stated weight percentages:

Carbon 0.02 to 0.06%

Silicon 0.25 to 0.7% Manganese 0.3 to 1.0% Nickel 2.0 to 3.0%

Chromium 15.0 to 17.0%

Molybdenum 0.8 to 1.2% Niobium 0.4 to 0.7% Nitrogen 0.02 to 0.04%

Iron, the balance with usual impurities in ordinary amounts.

2. An iron-chromium based alloy for use in an article involving stress corrosion and welding consisting essentially of the following elements in the stated weight percentages:

Carbon 0.05% Silicon 0.53% Manganese 0.57% Nickel 2.49% Chromium 15.65% Molybdenum 0.99% Nitrogen 0.028% Niobium 0.66%

Iron, the balance with usual impurities in ordinary amounts. 3. An iron-chromium based alloy for use in an article involving stress corrosion and welding consisting essentially of the Iron, the balance with usual impurities in ordinary amounts.

4. An iron-chromium based alloy for use in an article involving stress corrosion and welding consisting essentially of the following elements in the stated weight percentages:

Carbon 0.05% Silicon 0.50% Manganese 0.57% Nickel 2.49% Chromium l 5.65% Molybdenum 0.99% Niobium 0.66% Nitrogen 0.030%

Iron, the balance with usual impurities in ordinary amounts. 

2. An iron-chromium based alloy for use in an article involving stress corrosion and welding consisting essentially of the following elements in the stated weight percentages: Carbon 0.05% Silicon 0.53% Manganese 0.57% Nickel 2.49% Chromium 15.65% Molybdenum 0.99% Nitrogen 0.028% Niobium 0.66% Iron, the balance with usual impurities in ordinary amounts.
 3. An iron-chromium based alloy for use in an article involving stress corrosion and welding consisting essentially of the following elements in the stated weight percentages: Carbon 0.02% Silicon 0.49% Manganese 0.60% Nickel 2.50% Chromium 15.64% Molybdenum 0.97% Niobium 0.50% Nitrogen 0.039% Iron, the balance with usual impurities in ordinary amounts.
 4. An iron-chromium based alloy for use in an article involving stress corrosion and welding consisting essentially of the following elements in the stated weight percentages: Carbon 0.05% Silicon 0.50% Manganese 0.57% Nickel 2.49% Chromium 15.65% Molybdenum 0.99% Niobium 0.66% Nitrogen 0.030% Iron, the balance with usual impurities in ordinary amounts. 